The present invention relates generally to water-reducible film forming coating compositions and is more particularly concerned with flatted coating compositions comprising the combination of a water-miscible film forming resin, water and a finely-divided silica flatting agent.
In recent years substantial efforts have been expended in developing coating compositions containing little or no organic solvents. Such emphasis has, in large measure, been spawned by the desire to reduce the atmospheric pollution, fire, explosion and toxicity hazards which often attend the preparation and use of conventional coating compositions containing organic solvents. Accordingly, there have been developed a number of water reducible coating compositions based upon the combination of a water-miscible film forming resin and water as the predominant solvent, which compositions may be applied to a substrate and cured using conventional techniques and in which the resulting films are durable and bear many or all of the attributes of the prior art organic solvent reduced coating compositions.
It is known that flatting of coating compositions based on conventional organic solvents can generally be achieved by incorporation of an effective amount of a finely-divided silica into the formulation. This is normally accomplished during the mill paste stage of composition preparation wherein the composition solids, including the flatting agent, film forming resin, pigments, bodying agents and the like are milled together to form a well dispersed mill paste. Then, the mill paste is generally subjected to a "let-down" stage of formulation wherein it is diluted with the organic solvent to its finished solids concentration. Unfortunately, it has been found that this general procedure is relatively ineffective for purposes of flatting water-reduced coating compositions comprising a water-miscible film forming resin. Generally, it is found that little or no gloss reduction is achieved at conventional loadings of the silica flatting agent and/or that the amount of a given silica flatting agent required to achieve the desired reduction in gloss is so great as to be either uneconomic or as to cause other problems with the resulting coating composition. In accordance with the present invention, however, this problem has been resolved.